Evolution of BSI Multi-Collection-Gate Image Sensors -From Light-in-Flight imaging to Giga-fps Continuous Imaging-

This paper reviews evolution of the BSI MCG (Backside-Illuminated Multi-Collection-Gate) image sensors for ultra-high-speed imaging from the current status to the futuristic view. The structure originally employed a pwell for potential separation of the backside photoelectron conversion layer and the front-side circuit layer1). The test sensor achieved the frame interval of 10 ns2), and successfully captured flying light for the first time as a silicon image sensor3). By replacing the p-well structure for the potential separation by a silicon light/electron guide pipe or a convex pyramid charge collector, the temporal resolution will reach 50 ps to 100 ps3). The theoretical resolution limit is 11.1 ps as proved by Etoh, et al.4) All these image sensors work in the burst imaging mode with in-pixel signal storage. Further evolution is proposed with an additional cascade pipeline structure for the in-pixel analogue or digital storage in a stacked memory chip operating at 1 Gfps (t = 1 ns), and, hopefully, for continuous readout of the processed signals.